Hydrogen sulfide is a noxious, poisonous component of the off-gas of a number of industrial processes, e.g., the desulfurization of crude oil. Industrial off-gas is commonly used as a fuel in furnaces; however, if the off-gas has a high hydrogen sulfide content, its combustion produces substantial amounts of sulfur dioxide which also creates environmental problems. Hence, off-gas, high in hydrogen sulfide content, is undesirable for use as a fuel.
Several methods have been described for obtaining useful substances from off-gas-derived hydrogen sulfide, but only one, i.e., the Claus method, has had commercial significance. The Claus method is a two-step reaction which results in the production of water and elemental sulfur according to the following formulae; ##EQU1##
The Claus method produces one usable substance, sulfur, from the hydrogen sulfide, but discards the valuable hydrogen component in the form of water. Thus, the Claus process not only fails to utilize the full potential sulfide through complete combustion, as is the case when it is fully burned directly, but also fails to recover the hydrogen component.
It is known to thermally decompose hydrogen sulfide to hydrogen and sulfur; however, this reaction is highly endothermic and does not proceed far at temperatures below about 1200.degree. K. Direct methods of H.sub.2 S dissociation, such as that described in U.S. Pat. No. 2,979,384 in which H.sub.2 S is passed over a glowing tungsten filament, have not proven to be commercially feasable.
Reaction temperatures above 1200.degree. K. were heretofore considered impractical for effecting the thermal decomposition of hydrogen sulfide, and several catalytic methods have been described for decomposing hydrogen sulfide at lower temperatures in which reasonable yields are achieved by removal of product, i.e., sulfur, from the reaction mixture. U.S. Pat. No. 4,008,174 teaches reacting hydrogen sulfide with a metal sulfide to form a metal disulfide plus hydrogen, and subsequently regenerating the metal monosulfide from the disulfide using heat. In U.S. Pat. No. 3,856,925, a process is described in which hydrogen sulfide is decomposed in the presence of a metal sulfide, and the sulfur is removed from the metal sulfide, subsequently or concurrently, by carbon monoxide or nitrogen monoxide.